Red-emitting phosphors based on complex fluoride materials activated by Mn4+, such as those described in U.S. Pat. No. 7,358,542, U.S. Pat. No. 7,497,973, and U.S. Pat. No. 7,648,649, can be utilized in combination with yellow/green emitting phosphors such as YAG:Ce to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI)>80) from a blue LED, equivalent to that produced by current fluorescent, incandescent and halogen lamps. These materials absorb blue light strongly and efficiently emit in a range between about 610 nm and 658 nm with little deep red/NIR emission. Therefore, luminous efficacy is maximized compared to red phosphors that have significant emission in the deeper red where eye sensitivity is poor. Quantum efficiency can exceed 85% under blue (440-460 nm) excitation. In addition, use of the red phosphors for displays can yield high gamut and efficiency.
Processes for preparing the materials described in the patent and scientific literature typically involve mixing the raw materials and precipitating the product. Some examples of such batch processes are described in Paulusz, A. G., J. Electrochem. Soc., 942-947 (1973), U.S. Pat. No. 7,497,973, and U.S. Pat. No. 8,491,816. However, scale-up issues and batch to batch variation of properties of the product can be a significant problem. Moreover, batch processes produce materials having a broad range of particles sizes including relatively large particles. Large particles may clog dispensing equipment, causing problems in manufacturing LED packages, and also tend to settle unevenly, resulting in a non-homogeneous distribution. Therefore, processes for preparing the red phosphor that can yield a product having a smaller median particle size and a narrower particle size distribution, allowing better control over the final properties of the product while maintaining performance in lighting and display applications, are desirable.